The question has been fully answered, and you have been advised that it is not possible to get an STD in the scenario you describe. There is nothing more for our members to say about your no-risk event.
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STDs don't transmit through clothing (or any fabric) this way.
Have you had sex before? Oral sex? If your semen is yellow, you should get that checked by a doctor, but that's not a normal symptom of an STD. If it's yellow and smells bad, it could indicate an infection.
Yellow semen can indicate other health problems, though, so you should talk to your doctor. https://www.refinery29.com/en-us/yellow-semen-cum-color-causes